i'm not a professional photographer, just a pure crazy phot geek. i'm not technical enough to say which program is better and to tell you the truth, i tried processing the same picture in "default" settings on both programs and the pictures came out identical to my eyes, minus alittle shift in black/highlights due to the differences in each of the programs "default" settings. quality wise, it was the same.
i use photoshop CS2 because i'm more accustomed to it and it suits my digital darkroom needs perfectly. I think its really down to user preference, except for the few pros here that really know their ins and outs of digital processing.
so use whatever is more user friendly would be my advice.
and also, i've noticed that unlike my 5D, I just use the Jpeg files instead of processing the raw files. i notice most of my pictures rarely need much post processing. the M8 jpeg is very good at rendering shades and highlights to what it was really like when i shot the picture. I usually only go into Raw files these days when the whitebalance is off.
my two cents